"I speak English well."
"I speak English good."
Which of these is correct and why?
Well is an adverb and good is an adjective. The correct sentence is "I speak English well" because the the adverb well gives us more information about the verb speak. Using good, the sentence has to be "I speak good English" because good, as an adjective, modifies the noun English.
Link: Danny's 'Common Mistakes'
